For medium power applications, the power dissipated in the transistor makes the die temperature rise above that of its mounting base. The heat must be spread into the PCB and from there to the ambient environment. Designers of circuits using medium-power transistors often face the problem, that the conditions for power dissipation (Ptot) on the final PCB is different to those used for the maximum limits in data sheets. Data sheet Ptot limits for a SMD medium-power transistor are typically specified under the condition of the device mounted on single-layer PCB, with either standard footprint or increased collector mounting pad. Contrary to this condition, a modern circuit uses multi-layer PCBs are, with a significant benefit on heat management compared to single layer PCB. The power and ground planes in these boards spread the heat far beyond the package footprint and enhance heat transfer to the ambient environment.